MySQL Database indexing error

There has been a misunderstanding of the index, plus index of the disadvantage is that the increase in storage space, and increase the cost of adding and removing, but these I think for more and more good hardware, there is no big problem

So I always thought, in each field to add a separate index, so it is best, because the general card is dead, is a comprehensive select query, the relative increment of a single operation, even if the field plus one more than a lot of problems

However, it is important to ignore the problem that a query can only use one index

That is, even if you index all the fields, only one index is used, so the multi-field index

MySQL Database indexing error